In the oil industry where oil is extracted from one or more wells in an oil field, oil will be extracted together with water. The water has to be removed from the oil and this is mainly done by means of settling tanks in which the oil is permitted to settle through the action of the gravitational force. However, complex oil-water emulsions may develop during the extraction of the oil. For example, the removal of gas from the oil-water emulsion by means of gas-liquid cyclones might contribute to a more complex emulsion, which will be difficult to separate only by means of settling.
As an alternative or supplement to settling treatment is electrostatic treatment of oil and water has been used by the oil industry for many years to aid in the separation of water from an oil-continuous stream. Treating a water-in-oil emulsion by passing it through a high voltage electrostatic field has been shown to promote rapid coalescence or the water droplets, leading to rapid separation.